I've had several Dremel tools over the years and most of my work is in metal. When I bought my last one, I bought the heavy duty model. It is heavier but it is more to my needs in mettal work.
https://www.dremel.com/us/en/p/4000-2-32-f0134000fb
I think one of the reasons lots of people complain about short life on these bits is that they spin them too fast and burn them up. Once the first step penetrates, I slow the bit down. I get pretty good life out of mine.
Definitely need to take the weight of the motor off the shaft/coupling. Some sort of foot bracket that can be shimmed is commonly used. Misalignment will eventually break the shaft. A Lovejoy/Magnalloy type coupling is more forgiving than the chain and sprocket type...
I like to use them when building engines, transmissions, etc. You can feel if a fastener and thread are not meshing properly and you can tighten all the fasteners around a pan or head to roughly the same torque before torquing them. I just don't trust power wrenches for that work.
Media blasting cabinet is the best and easiest way to remove scale. It's much faster than a grinder of any kind. You can also use it to remove rust, paint, etc on parts you are repainting. Use aluminum oxide media.
I bought a 1/4" Tekton stubby ratchet about a year ago and I love the thing, EXCEPT for one thing. The quick release does not retain my Craftsman sockets and extensions. I tried disassembling it but the QR part doesn't appear serviceable. So, I blew brake cleaner through it from the end and the...